At least 13 people were killed and dozens injured in gun and bomb attacks at the Iranian parliament and Ayatollah Khomeini’s shrine in Tehran on Wednesday. The attacks were later claimed by Islamic State (IS, formerly ISIS/ISIL).

Five attackers were Iranian citizens who had joined IS before returning to Iran in summer 2016, the Iranian Intelligence Ministry reported on Thursday, according to IRNA news agency.

“The five known terrorists... after joining the IS terrorist group, left the country and participated in crimes carried out by this terrorist group in Mosul and Raqqa,” the ministry said, adding that in 2016 they returned “to carry out terrorist attacks in the holy cities of Iran.”